1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing cell selection in a wireless communication system.
2. Related Art
The Third Generation Partnership Project (3GPP) Long Term Evolution (3GPP LTE) which is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) is introduced as 3GPP Release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) for the downlink, and single carrier frequency division multiple access (SC-FDMA) for the uplink, and adopts multiple input multiple output (MIMO) with up to 4 antennas. Research is now underway on 3GPP LTE-Advanced (LTE-A), which is a major enhancement to 3GPP LTE.
Cell selection and cell reselection are processes of selecting a serving cell for serving a user equipment (UE). The UE measures the serving cell and/or its neighboring cells, and selects a best ranked cell.
Closed subscriber group (CSG) services, which are services that can be provided only to a certain group of subscribers, have been introduced to improve quality of service. A base station (BS) capable of providing CSG services is referred to as a Home eNodeB (HNB), and a cell serving CSG members is referred to as a CSG cell. The basic requirements regarding CSG services are as disclosed in 3GPP TS 22.220 V1.0.1 (2008-12) “Service requirements for Home NodeBs and Home eNodeBs (Release 9)”.
In CSG cells where CSG services are currently provided, channel environment may deteriorate. Thus, the quality of services may sometimes be worse in CSG cells than in non-CSG cells.
In, systems for supporting CSG services, there is a need for a method and apparatus to take a channel environment into consideration when performing cell selection.